Description of problem:
When calling shutdown -r/reboot/init 6 parent process should be allowed to terminate graciously like on RHEL6 where systemd is not used.
Version-Release number of selected component (if applicable):
systemd-219-19.el7.x86_64
How reproducible:
always, deterministic
Steps to Reproduce:
1. execute bash script with following content (as root):
#!/bin/bash
shutdown -r now
touch /root/test
2. ls /root/test
3. file /root/test does not exist
4. shutdown -r now can be replaced with either reboot or init 6, behavior is not changed
Actual results:
File /root/test does not exist as parent process is not allowed to terminate graciously.
Expected results:
File /root/test should exist like it does when executed on RHEL 6.7 machine (it gets created on RHEL 6.7 in all 3 cases).
Additional info:
This behavior is root cause of following bug: https://bugzilla.redhat.com/show_bug.cgi?id=1260527

Well, your reproducer should not work anywhere because:
1) Init will send you sigterm immediately which will kill your script.
2) Termination of login process will end up with sighup, which will kill your script.
If you try to block those signals:
[root@localhost ~]# cat test.sh
#!/bin/bash
logger "XXXXX-my pid: $$"
trap "echo nope" SIGTERM SIGINT
reboot &
sleep 2
echo whoohooo > /root/out
[root@localhost ~]# nohup ./test.sh
The /root/out will be created. I guess it worked for you on rhel6 only because the shutdown was pretty slow there.